Electric haircutting appliances are generally known and include trimmers, clippers and shavers whether powered by main supplied electricity or batteries. Such devices are generally used to trim body hair, in particular facial and head hair to allow a person to have a well-groomed appearance. These devices can, of course, also be used to trim pet hair or any other type of hair.
Conventional haircutting devices comprise a main body forming an elongated housing having a front or cutting end and an opposite handle end. A cutting blade assembly is disposed at the cutting end. The cutting blade assembly usually comprises a stationary cutting blade and a moveable cutting blade. The moveable cutting blade moves in a reciprocal, translatory manner relative to the stationary cutting blade. The cutting blade assembly itself extends from the cutting end and is usually fixed in a single position relative to the main body of the hair clipper, such that the orientation of the cutting blade assembly is determined by a user orientating the main body of the device.
In common cutting blade units the cutting force driving the moveable cutting blade is usually transmitted through an electric motor driven eccentric. This eccentric is driven by an electric motor in a rotary manner. The rotary movement of the eccentric is then translated via a so-called driving bridge, which is connected to the moveable cutting blade, into the resulting reciprocal, translatory movement of the moveable cutting blade.
A common problem that occurs in such hair clipping systems is the so-called pulling effect. The pulling effect is an unwanted lifting of the moveable cutting blade from the stationary cutting blade, which may especially occur during heavy load hair cutting. A reason for this pulling effect is the occurrence of a torque or twisting action on the moveable cutting blade that may cause a tilt of the moveable cutting blade. The evenness of the stationary and the moveable cutting blade, i.e. the evenness of the top surfaces of the stationary and the moveable cutting blade, have a strong influence on the redoubtable pulling effect. It is therefore desired that the top surfaces of the cutting blades are as even as possible. However, in common cutting units the manufacturing process does not allow to have perfectly even cutting blades. The best results in manufacturing are reached with an additional grinding step at the end of the manufacturing process. Even with such an additional grinding step the evenness deviation is, however, in a range of about 5 μm for each cutting blade. In the worst case the warpages of both cutting blades add up positively, so that an evenness deviation of up to 10 μm or more could result therefrom. This causes a so-called diagonal warpage in one or both cutting blades during the assembly.
As soon as the moveable cutting blade is driven in the above-mentioned reciprocal manner, a small gap between the two cutting blades will occur. This can cause the above-mentioned fishtailing, lifting or tilting of the moveable cutting blade, which is known as pulling effect. This pulling effect especially occurs under heavy load conditions, e.g. maximum quantity, tightness, length, thickness and/or shape of the hairs. For every home user, professional hair and beard trimmer and also for the hair cutting of pets the pulling effect is redoubtable as it may generate remarkable hurt by pulling hairs into the device instead of cutting them. The pulling effect therefore also degrades cutting performance and may increase noise, wear and tear. Expertise for the above-mentioned pulling effect is known from the applicant's research as well as from other professionals in hair clipping.
A lot of prior art hair clipping devices try to overcome this effect by applying a very strong spring, which presses the two cutting blades against each other. The force applied by the spring shall impede a lifting or tilting of the moveable cutting blade. The spring force is also used to compensate for the manufacturing-related warpages within the cutting blades.
An example of such a cutting unit for a hair clipping device is known from U.S. 2011/0061241 A1. Therein, an adjustable screw is used with which the pressure between the stationary cutting blade and the moveable cutting blade may be manually adapted. However, if the pressure between the stationary cutting blade and the moveable cutting blade is increased, the friction between the two cutting blades will be increased as well. This increased friction often makes oiling necessary. Besides that it increases the abrasion of the two cutting blades.
The increased friction also requires the appliance of an enlarged electric motor. Such an enlarged electric motor is on one hand expensive and on the other hand also voluminous. It increases the overall size of the hair clipping device as well as it increases the production costs. Apart from that the power consumption of such enlarged electric motors is also higher than for hair clipping devices using smaller electric motors. This is especially disadvantageous for battery-driven hair clipping devices which in turn have shorter operating times.
EP 1 120 206 A1 discloses a blade block of a hair cutter including a fixed blade, a movable blade reciprocating with respect to the fixed blade, and a blade base to which the fixed blade and the movable blade are attached. The fixed blade and the movable blade are assembled with a reciprocating guide unit into a blade unit. The reciprocating guide unit guides the movable blade to reciprocate with respect to the fixed blade. The blade block includes an insertion opening. A mounting unit is provided to mount the blade unit to the blade base by inserting the blade unit into the insertion opening so that a cutting edge is exposed to the outside of the blade block.